1. Field of the Invention
The present invention relates generally to assembly line piece marking tools and, more particularly, to a positive piece engagement indicator for marking tool.
2. Description of the Related Art
Current regulation require that various component assemblies that comprise a motor vehicle be scribed with a unique, identifying indicia that can allow the manufacturer or law enforcement to compare or trace the source of such component assemblies. With the current state of automation on vehicle assembly lines, such marking or scribing is also currently done, generally, in an automated fashion. For example, as a vehicle frame assembly is fabricated and conveyed down an assembly line for insertion of drive train or attachment of body or cabin components, a marking tool will scribe, etch, or stamp a unique vehicle identification number at a specific location on the frame. This number will correspond with a similar number scribed, etched, or stamped on the engine components as well as the body or cabin components.
In the related art, two general types of marking tools are generally commercially available and used for this process. These can be broadly classified as impact type marking tools, and etch type scribing tools.
Impact type marking tools generally operate by driving an impact pin into a collision with the metal workpiece, thereby leaving an impression. Although multiple impact pins, each having a striking surface shaped like a different letter or number can be used, the most common of these types of impact marking devices utilizes either a single pin that can move within a grid of positions, or an array of such pins. By leaving a series of aligned impressions, characters can be formed by this series of “dots”. Examples of such a system currently commercially available include the Telesis Controls Corporation pin matrix embossing apparatus described in U.S. Pat. No. 4,506,999.
Etch type scribing devices perform an equivalent function operating on a different principle. By guiding a scribing tip or cutting blade, a character is gouged or etched into the surface of the metal. Examples of such a system includes the BORRIES™ scriber marking system, that provides a constant, pressurized impact and relative motion between tool tip and work surface. This is generally known as a scriber type marking device. An alternate type of etching device is known that can be considered a cross between impact printer and scriber, providing a pressurized impact and relative motion between a vibrating or reciprocating stylus and a work surface. Examples of such a system include the Micro-Percussion Marking Device as supplied by TEKNIFOR™.
Common to both types of method are the use of a metal tipped marking implement contacted and penetrating a metal part surface.
Problems currently exist in the use of any currently, commercially available system that generally involve verification of the stamping or scribing process. The main problem using either type of system is the result of inadequate piece engagement relative to the marking device. In use of the impact type marking tools, should the impact pin fail to be properly aligned, or otherwise fail to properly collide and penetrate the surface of the metal workpiece, an inadequate impression is left, or possibly no impression at all. Similarly, in the use of scribe type marking systems, should the scribing tip or cutting blade fail to contact the surface to be marked continuously through the etching process, the same deficient results occur.
Sundry reasons may exist that result in such errors. Movement of the assembly line, placement of the piece on the assembly line, movement of the marking tool, rotational misalignment of the piece or marking tool, or any condition that can result in inadequate placement of the marking tool relative to the piece to be marked will cause the same overall result. Attempts to correct for the foregoing problems have been few and limited. Currently, outside manual inspection, the only available system to verify or check the marking process in an automatable manner has been the of computerized vision system technology to visibly inspect the marked reference characters after scribing or impacting. Because, by necessity, each reference indica is inherently unique overall, such vision systems are complex, unreliable, and very expensive to install and operate.
A search of the prior art did not disclose any patents that read directly on the claims of the instant invention; however, the following references were considered related.
U.S. Pat. No. 4,883,291 issued in the name of Robertson discloses dot matrix formed security fonts.
U.S. Pat. No. 5,893,668 issued in the name of Harrison et al., discloses a method for optimizing font marking.
U.S. Pat. No. 5,319,352 issued in the name of Robertson et al. discloses a speed monitoring of in-plant, operator controlled vehicles.
U.S. Pat. No. 5,316,397 issued in the name of Robertson et al. describes a marking apparatus with multiple marking modes.
The following two patents, both assigned to Rockwell, appear to be directed at position detection, albeit for rotary based motion control:                U.S. Pat. No. 5,712,574 issued in the name of Street discloses an apparatus for position detection and verification thereof using pulse patterns having sequentially unique properties.        U.S. Pat. No. 5,350,955 issued in the name of Street discloses an apparatus for position detection and verification thereof using pulse patterns having sequentially unique properties.        
Additional patents have been provide in order to indicate the general nature and direction such “detection” systems have taken in other ancillary arts:                U.S. Pat. No. 5,393,967 issued in the name of Rice et al. discloses a method and apparatus for non-contact reading of a relief pattern.        U.S. Pat. No. 5,397,872 issued in the name of Baker et al. discloses a weld monitor system.        U.S. Pat. No. 5,231,675 issued in the name of Sarr et al. discloses a sheet metal inspection system and apparatus.        
Consequently, a need has been felt for providing an apparatus and method which allows for verification of contact between impact or scribing tool and the work surface to be marked or scribed.